The present disclosure relates generally to the treatment of patients having treatable medical conditions using weak (i.e., low-intensity) low-frequency (i.e., several Hz) magnetic fields (WMF). More particularly, this disclosure relates to using WMF to apply therapy in a target volume of biological tissue, such as a tumor or a heart afflicted with arrhythmia.
In the past, the possibility of treating cardiac arrhythmias with the application of WMF has been proposed. In particular, the concept of using a magnetic field generator as a regulator of atrial fibrillation has been previously disclosed. It is now accepted that the effect of a magnetic field on an excitable cell's membrane works through influencing the kinetics of potassium ions. This happens in the neurons as well as in the cardiac myocytes (cardiac muscle cells), which generate the electrical impulses that control the heart rate. Field intensity and modulation frequency have been shown to be important determinants in WMF causing cellular K+ efflux. The K+ channel modifies other ion transporters, such as the calcium and sodium channels. Magnetic fields induce movements of K+ ions across the cell membrane, which affects the shifts of K+ ions through openings in their membrane channels.
Among the diverse excitable cells within the heart are the highly specialized pacemaker cells in the SA node and the AV node, which have spontaneous depolarization due to slow outward efflux of K+ ions until reaching the threshold of excitation. Atrial cells and ventricular cells have different electrophysiological properties, yet both possess K+ channels (in addition to Na+ and Ca2+ channels). But, in a pathological state, they may exhibit an automatic excitability to fire rapidly or irregularly, causing cardiac arrhythmias. This is one mechanism of cardiac arrhythmia.
A WMF (as weak as is still capable of affecting the flux of K+ ions across the cell membranes) can ignite a self-propagated process of Ca+, K+ and Na+ ion shifts. It depends on the modes of WMF stimulation (frequency, intensity and configuration) and/or an additional external intervention (such as the application of drugs), to determine if the cell will discharge following its excitation or be further inhibited. It is known from in vitro experiments that WMF can induce activation, reactivation and inhibition of the excitable cells. Weak magnetic fields can have a negative chronotropic effect on cardiac pacemaker cells and can be used continuously or intermittently to alleviate atrial fibrillation.
In order to facilitate non-invasive therapy of target organs (such as the heart) or localized regions inside the human body (such as a tumor), it is important that the magnetic field be concentrated or focused at the area requiring treatment. U.S. Pat. No. 8,396,566 discloses the use of spiral coils to generate magnetic fields for the purpose of resynchronizing a heartbeat. U.S. Published Patent Application No. 2005/0222625 discloses a coil array forming part of a non-invasive pacemaker. Although these references disclose that focused magnetic fields can be directed toward a target site in a heart (such as the SA node, the atria, the left ventricular septum, etc.) to provide non-invasive therapy, neither reference discloses any mechanism or means for directing and focusing the magnetic field to form a magnetic beam.
Accordingly, there is a need for apparatus for directing and focusing magnetic fields at a target site inside biological tissue.